The present invention relates to a controller for material forming machines such as metal forming machines. The illustrated embodiment relates particularly to a controller for cold heading machines.
In the fastener industry, steel wire is often pressed, rather than cut, as an initial step in making workpieces such as screws, for example. In this pressing, known as cold forming or cold heading, a cold heading machine is used in which a moving die hits a wire slug in a stationary die, typically at a rate of 100 to 450 workpieces per minute.
Cold heading machines have often in the past required operators to determine whether the machine should be stopped due to any one of a variety of causes, such as inadequate quality of the incoming wire, blockage of the feeding mechanism, depletion of the wire supply, blockage of a die by misfed parts, tool breakage, excessive tool wear, or completion of the batch.
Recently, at least one attempt has been made to automate the control of cold heading machines. One known controller uses a microprocessor to determine, it is believed, whether a prescribed tolerance has been exceeded in the force applied to the wire by the cold heading machine. If this tolerance is exceeded, the controller shuts off the machine. An important problem with this known controller is that it is prone to shut down a machine unnecessarily if the tolerance is reasonably set when a "hard spot" is encountered in the wire. Such a "hard spot" can for example, correspond to a localized increase in wire size at a point where two reels of wire have been joined, and can result in a single workpiece or only a small member of workpieces being beyond tolerance. In the present commercial context, hard spots are often quite widely spaced, and it is often commercially acceptable to provide a certain number of parts beyond tolerance in a given run, so long as a minimum number of parts within tolerance are produced. As a result, an operator using this machine controller will: (1) suffer an unnecessary interruption of machine operation each time a hard spot in the wire is encountered; or (2) manually adjust the tolerance to wide margins and run an excess number of parts, resulting in excessive scrap; or (3) use wide tolerances without an excess number of parts, thereby risking failure to produce the prescribed minimum number of parts within tolerance. Each of these options brings with it commercial disadvantages.
One object, therefore, of the present invention is to overcome the very many problems with such known controller and to provide an improved controller which will permit a hard spot in the wire to be processed unless it results in an excessive number of out-of-tolerance pieces. A further object is to provide a less expensive controller: currently the cost of the known microprocessor-based controller is $10,000-$15,000 per cold heading machine. One object of the present invention is to reduce this cost significantly.
Another object is to simplify the operation of the controller for the machine operator, and to provide means for effective communication between the machine operator and the controller.